The present invention relates to a method of manufacturing roofing felts, cap sheets, base sheets and similar built-up roofing products and, in particular, to a method of manufacturing such built-up roofing products in which the fibrous roofing mats are moisturized, preferably with steam (water vapor) prior to the application of a bituminous coating (an asphalt or coal tar coating) to reduce the amount of the bituminous coating required to produce the built-up roofing products.
Built-up roofing products, such as roofing felts, cap sheets and base sheets, are manufactured by coating roofing mats with a hot bitumen, such as asphalt or coal tar, to impregnate or saturate the roofing mats with the hot bitumen. After a roofing mat has been coated with the hot bitumen, the coated roofing mat is cooled to cool the bitumen; one or both major surfaces of the coated roofing mat are normally coated with a release agent, such as a liquid parting agent or a sand surfacing, to keep the bitumen from the coated roofing mat from adhering to the equipment rolls and to keep adjacent convolutions of the coated roofing mat from sticking together when wound up into a roll; and the finished product, the roofing felt, cap sheet or base sheet, is typically wound up into a roll for storage and shipment.
Roofing felts, cap sheets and base sheets are typically used to form built-up roof membranes on roof decks wherein plies of these built-up roofing products and hot asphalt or bitumen are applied to the roof decks to form the built-up roof membrane. The hot asphalt or bitumen is applied to the roof deck by mopping the asphalt or bitumen onto the deck and plies of the built-up roofing products which function to stabilize the mopped asphalt or bitumen and keep the asphalt or bitumen, which is otherwise an excellent water barrier, from cracking and leaking.
The roofing mat used in the manufacture of built-up roofing products, such as roofing felts, cap sheets and base sheets, is typically made of randomly oriented glass fibers which are laid down in a dry process or a wet process. Preferably, the roofing mat is made of randomly oriented glass fibers that have been laid down in a wet process to form the mat. Glass fiber roofing mats, made by a wet process such as a Fourdrinier type of process, are preferred because these wet process mats have an extremely consistent fiber distribution and density with fine, uniform perforations that are large enough to provide adequate venting during roof application, but small enough to properly stabilize the built-up roof membrane bitumen.
Glass fiber roofing mats, made by the dry process, have a porous, lace-curtain appearance with many relatively large, irregularly sized openings that may not properly stabilize the built-up roof membrane bitumen. Thus, while glass fiber roofing mats made by a dry laid process may be used in the method of the present invention to form built-up roofing products, roofing mats made by the wet laid process are preferred.